Query about addressing agents

[Dontrocktheboat]

Hi, I have sent my novel off to a few agents, though with no success so far! It just occurred to me that I have never really checked how to address an agent in the covering letter, I have just been using first names (as the world in general seems so informal these days!) but now wondering if this might be presumptuous and should use Mr / Ms?? Be grateful if anyone can tell me what is accepted etiquette!

I used their first names, but I doubt it matters either way as long as you don't put Dear Sir!

Thanks (again!) sticking with first names I think!

I think email lends itself to first names while letters surnames.

Ps- I am no debretts!

Thanks all - yes agree think sounds a bit weird to use formal address in email!